X-ray and EUV sources based on emission from a laser produced plasma in a target jet are becoming increasingly important since they provide a high-density regenerative target in combination with negligible debris operation. To this date, commercially available glass nozzles have primarily been used to produce the target jet, resulting in limited flexibility in the choice of jet dimensions, speed and jet material.
X-ray and EUV sources of the above-mentioned kind feature high flux and brightness, allow long-term operation without interruption and emit narrow bandwidth radiation appropriate for zone-plate optics. Furthermore spectrally tailored emission for a specific application can be produced by selecting a target material with proper elemental contents.
Methods for generating x-ray or EUV radiation via laser produced plasma emission are known in the prior art. For example, U.S. Pat. No. 6,002,744 discloses a method wherein a target is generated in a chamber and at least one pulsed laser beam is focused on the target in the chamber to produce the radiating plasma.
Until now, these target jets have been produced using commercially available tapered glass nozzles. Unfortunately these nozzles have a fixed diameter and the range of usable target materials is limited since several interesting target materials have shown to dissolve some parts of the nozzle.
Other problems are associated with the prior art technology regarding the way the target material is supplied to the jet-forming nozzle.
For cryogenic applications, wherein a material that is gaseous at room temperature and atmospheric pressure cooled to liquid state, the cooling of the target material must be done within the chamber in which the plasma is to be produced.
Furthermore, when an organic material such as e.g. alcohols are employed, there is a tendency of pollution of the passageways in the supply system for the target material. The reason is that many carbon based materials may dissolve parts of the equipment or seals used, such that the target material contains fragments or substances that may then clog the jet-forming nozzle. This problem is accentuated by the numerous joints in the supply system for the target material. Many inorganic materials, which may have aggressive properties, can lead to similar problems.
In addition, rather large volumes of target material must be handled and pressurized. Some target materials used are expensive, and for this reason alone the volume that has to be handled should be kept at a minimum. Furthermore, the target material must be kept at a desired pressure and temperature, which of course is rendered more difficult if dealing with large volumes.
Consequently, there is a need for improved methods and arrangements for generating x-ray or EUV radiation via plasma emission.